1. Field of the Invention
This invention is directed toward apparatus and methods for separating fluids of differing specific gravities, and more particularly directed toward apparatus and methods for separating a high volume flow of fluid comprising a mixture of air and water into an essentially dry air component and a pure water component.
2. Background of the Art
Many industrial, scientific and operational procedures require the separation of a composite fluids into components of differing specific gravity which comprise the composite.
The oil and gas industry is based upon the production of liquids from the earth which usually consists of a mixture of liquid and hydrocarbon gas. Furthermore, the liquid usually consists of a mixture of hydrocarbons (oil or gas condensate) and water (fresh or saline). The produced fluid must be separated not only to recover commercial quantities of hydrocarbon in the liquid and gas phases, but also to render the byproduct (produced water) in a form in which it can be disposed of in an economically and environmentally acceptable manner. The chemical, pharmaceutical, food and countless other industries employ apparatus and methods for separating composite fluids into their components or "phases" of differing specific gravities. In most commercial separation procedures, it is economically desirable that the procedure be "high volume" in that large quantities of composite fluid can be separated in a relatively short period of time. It is also desirable that the separation apparatus be relatively inexpensive to fabricate, maintain and operate.
Scientific research often requires that composite fluids or slurries be separated into components of differing specific gravities. Often, separation of components of almost equal specific gravity is required. In most scientific separation procedures, precision and accuracy are the primary criteria, and the rate at which separation occurs is usually secondary. Although it is desirable to minimize the cost of scientific separator equipment, fabrication costs, maintenance cost and operation costs of this equipment is usually not as critical as in the case of commercial separator equipment.
Numerous manufacturing and production operations involve the separation of composite fluids into gas and liquid components. As discussed previously, hydrocarbon production requires the separation of gas and liquid hydrocarbons, and the further separation of water from the produced fluid. Operationally, water separated from liquid hydrocarbon must meet certain regulatory standards before the water can be discharged into bodies of surface water or reinjected into an underground earth formation. Copending application Ser. No. 08/757,242 filed on Nov. 27, 1996 now abandoned and assigned to the assignee of the present application discloses apparatus and methods for temporarily lowering the ground water level in the vicinity of the an excavation, such as a pipeline trench, in order to prevent the ground water from flooding the excavation. The technique involves applying a vacuum to a series of suction pipes sunk around the periphery of the excavation and sunk to a depth below the maximum depth of the excavation. The vacuum pump draws ground water from the earth in the immediate vicinity of the excavation, up through the suction pipes and into a main flow line which empties into a holding vessel. The ground water level is thereby temporarily lowered in the vicinity of the excavation, and flooding of the excavation is thereby prevented until work to be done within the excavation can be completed. Some of the suction pipes may not penetrate the level of the ground water. Furthermore, "cavitation" can occur in fluid drawn through suction pipes which do penetrate the ground water level. The result is that the fluid drawn to the surface usually consists of a mixture of water and air. It the drawn water phase is to be reinjected into the ground water table, it is usually required that it be reinjected as drawn (i.e. without air). The drawn fluid must, therefore, be separated into an air and a water component before disposal.
Gravity separators have been used commercially for decades to separate composite fluids with components of differing specific gravities. Separator tanks are typically cylindrical. Composite liquid is typically pumped into the tank where it remains for a time sufficient to allow components of differing specific gravity to separate under the influence of gravity. The separator tank has as least two outlets for withdrawing separated fluid components. For purposes of discussion, assume that the composite fluid comprises a liquid phase and a gas phase. One outlet is positioned at, or very near, the bottom of the tank and is used to withdraw the heavier liquid phase which settles to the lower portion of the tank. A second outlet is positioned at or very near the top of the tank and is used to withdraw the component of lower specific gravity which is, in this example, gas which collects at the top of the tank. It should be noted that gravity separators can contain more that two outlets, and can be used to separate composite fluids containing more that two components. A notable example is the previously discussed fluid produced by the hydrocarbon industry which typically comprises water, liquid hydrocarbon (oil and gas condensate), and natural gas. Gravity separators are considered to be "low volume" separators in that time is required for components to "gravity" separate, especially if there is little difference in specific gravities. In order to increase volume through-put, gravity separators can be quite large, very immobile, and expensive to fabricate and to maintain.
Other approaches have been applied to the separation of composite fluids in order to overcome some of the disadvantages of gravity separators. One such approach involves forcing the fluid to flow, under high pressure, in a helical path thereby separating components of differing specific gravity using centrifugal force. These devices are shaped somewhat like a rifled gun barrel and are known generically, at least in the petroleum industry, as "hydroclones". Hydroclones are applicable to separating components with significantly different specific gravities, such as water and free gas. The physical size of a hydroclone require to separate a given volume of composite liquid-gas fluid is much smaller than a gravity separator required to process the same volume. As an example, an average sized person can lift a hydroclone which will process the same volume of "two-phase" fluid as a gravity separator the size of a bed room. Hydroclones are, therefore, generally considered to be "high volume" separators, at least for their relative size. Hydroclones are not, however, efficient at separating fluid components such a gas containing liquid droplets or mist.
Other centrifugal systems have been developed to separate components of fluid mixtures, wherein the specific gravities of the components differ by as little as a few thousandths. These are low volume devices, and motor driven at tens of thousands of revolutions per minute. These are typically large and very expensive to fabricate, operate, and maintain. As a result, these separators are more ideally suited for scientific applications, or for specialty type manufacturing processes.
In summary, some separator technologies available in the prior art are directed toward low volume output, or are required to be physically large and very immobile for high volume output. The gravity separator is an example of this technology. Other technologies are directed toward high volume output but require substantial differences in specific gravities of the components. The hydroclone separator is an example of this technology. Still other technologies are directed toward precise and accurate separation of fluid phases with slightly differing specific gravities, but are expensive to fabricate and to maintain and to operate. The centrifugal separator is an example of this technology.
An object of the present invention is to provide apparatus and methods which can separate high volumes of composite fluid into components of significantly differing specific gravity such as air and water.
An additional object of the present invention is to provide apparatus and methods for extracting the gas component from a gas-liquid composite fluid, wherein the gas component is essentially free of liquid and therefore considered "dry".
A further object of the present invention is to provide apparatus to meet the previously defined objects, wherein the apparatus is physically small, mobile, and relatively inexpensive to fabricate, to operate and to maintain.
A still further object of the present invention is to provide apparatus to meet the previously defined object which is rugged and highly reliable from an operational viewpoint.
There are other objects and applications of the present invention which will become apparent in the following disclosure.